Polyethylenimine-Modified Magnetic Chitosan for the Uptake of Arsenic from Water

Round 1

Reviewer 1 Report

Investigation of adsorption capacities of magnetic nanoparticles in as prepared samples of model compounds As(V) and As(III) is presented in the manuscript. The information provided can be useful for the science and practice, as well. Therefore, this work contains interesting information for the journal readership. The MS is generally well written with a logic structure. Research motivations and state of art are clearly highlighted in the introduction section. Methods applied in research are given in detail. Results are discussed in detail with relevant references.

Even though there are not new and significant results, the manuscript contains valuable and well-structured experimentation that could be useful for a wide community of professionals. For this reason, I consider to accept this manuscript after consideration of the following comments:

1. Manuscript present some grammar and spelling mistakes, I recommend the authors to perform an exhaustive revision throughout the text.
2. Underscore the scientific value-added to your paper in your abstract. The abstract should clearly state the essence of the problem you are addressing, what you did and what you found and recommend. What are the highlights of your work?
3. L22: avoid the use of terms like novel.
4. In the sentence L70-72 “Among those, Fe3O4… and low toxicity.” refer this article: Gallo-Cordova, A.; Veintemillas-Verdaguer, S.; Tartaj, P.; Mazarío, E.; Morales, M.d.P.; Ovejero, J.G. Engineering Iron Oxide Nanocatalysts by a Microwave-Assisted Polyol Method for the Magnetically Induced Degradation of Organic Pollutants. Nanomaterials 2021, 11, 1052. https://doi.org/10.3390/nano11041052
5. L226: include standard deviation of the particle size value. Include the particle size distributions in Figure 2. There is no significant change between Figure 2a and 2b, they cannot be used to prove the CS grafting.
6. Figure 2: please provide better TEM images of Fe3O4/CS/PEI. The micrograph itself contributes nothing, it is not possible to claim that you have core-shell structures by showing just one particle. Provide also the shell size distribution.
7. L232: you cannot claim particles are homogenous with just one micrograph. Please include particle size distribution considering at least 200 particles.
8. L233-234 it is not correct to say Fe3O4 are bigger with no evidence, it is possible that the average particle size is within the error.
9. Figure 3 I consider the two images does not belong together in the same Figure.
10. pH effect: It would be interesting to see arsenic speciation diagram compared to zeta potential titration graph of the adsorbent.
11. I suggest authors to send Figure 5b and 5c to supporting information. Table 1 provides enough support for the kinetic and isotherms modelling. The same with Figure 6b and 6c.

Author Response

1. Manuscript present some grammar and spelling mistakes, I recommend the authors to perform an exhaustive revision throughout the text.

 The Manuscript was revised and grammar and spelling mistakes were corrected

2. Underscore the scientific value-added to your paper in your abstract. The abstract should clearly state the essence of the problem you are addressing, what you did and what you found and recommend. What are the highlights of your work?

The abstract was rewritten as required by the reviewer

3. L22: avoid the use of terms like novel.

The word "novel" was omitted from the manuscript

4. In the sentence L70-72 “Among those, Fe3O4… and low toxicity.” refer this article: Gallo-Cordova, A.; Veintemillas-Verdaguer, S.; Tartaj, P.; Mazarío, E.; Morales, M.d.P.; Ovejero, J.G. Engineering Iron Oxide Nanocatalysts by a Microwave-Assisted Polyol Method for the Magnetically Induced Degradation of Organic Pollutants. Nanomaterials 2021, 11, 1052. https://doi.org/10.3390/nano11041052

This reference was added in the text and in the references list

 L226: include standard deviation of the particle size value. Include the particle size distributions in Figure 2.

The SD values were added to the particle size values and the particle size distribution was added to Fig.2.

There is no significant change between Figure 2a and 2b, they cannot be used to prove the CS grafting.

This may be attributed to the small differences between the Fe3O4 NPs and Fe3O4/CS in size. The same results was observed in the Ref.(Li, G.-y.; Jiang, Y.-r.; Huang, K.-l.; Ding, P.; Chen, J. Preparation and properties of magnetic Fe3O4–chitosan nanoparticles. Journal of alloys and compounds 2008, 466, 451-456.

6. Figure 2: please provide better TEM images of Fe3O4/CS/PEI. The micrograph itself contributes nothing, it is not possible to claim that you have core-shell structures by showing just one particle. Provide also the shell size distribution.

We repeated the TEM images many times and this is the best one we got. The shell size distribution required large number of particles with core-shell structure and this not available with the got TEM image.

 L232: you cannot claim particles are homogenous with just one micrograph. Please include particle size distribution considering at least 200 particles.

The particles size distribution was added (please see Fig.2d)

 L233-234 it is not correct to say Fe3O4 are bigger with no evidence, it is possible that the average particle size is within the error.

      The nanocomposite has the higher size than Fe3O4 and Fe3O4/CS and this was clear also from XRD results.

 Figure 3 I consider the two images does not belong together in the same Figure.

     The two images in Figure 3 were separated in two figure 3 and figure 4.

 pH effect: It would be interesting to see arsenic speciation diagram compared to zeta potential titration graph of the adsorbent.

We thank the reviewer for this remark. In this section, we have highlighted the effect of the pH on the adsorption of As (III) and As (V) ions over the surface of Fe3O4/CS/PEI nanocomposite. Now, we are planning to study the nanocomposite use for the removal of various ions including As. The behaviour of the adsorption of these ions will be compared. Also, we will arrange to measure the zeta potentials at different pH value. We will draw the ion speciation diagrams and will be compared to zeta potential titration graphs.

11. I suggest authors to send Figure 5b and 5c to supporting information. Table 1 provides enough support for the kinetic and isotherms modelling. The same with Figure 6b and 6c.

We thank the reviewer for this suggestion. However, we think that the both figures and tables are important and must be included in the main manuscript.

Reviewer 2 Report

The Authors described studies concerning on absorption of arsenic from water using polyethylenimine modified magnetic chitosan. The water purification from toxic elements is extremly important nowadays. The manuscript could be published in Applied Sciences after minor revision.  Below, several aspects  have mentioned, which should be corrected and some doubts should be explained.

 

1. I suggest to add information about recognized phases in Fig. 1b. Moreover, the XRD pattern does not present peaks but reflexes. Please change it in the text.
2. Why 0.89 was chosen as correct for these studies?
3. I suggest to add some zoom picture of fig. 3a in order to show the changes in coercivity.

 

Generally, the Authors did an excellent work. However it could not be published in present form in Applied Sciences. I recommend minor revision.

Author Response

I suggest to add information about recognized phases in Fig. 1b. Moreover, the XRD pattern does not present peaks but reflexes. Please change it in the text.

Statements were added in this section to more discuss Fig 1b

The word "peaks" was replaced by "reflexes"

Why 0.89 was chosen as correct for these studies?

According to Debye-Scherrer equation, K is grain shape constant. In this study k=0.89 for spherical shape. In this study, the shape of these particles is considered spherical as reported in the literature.

I suggest to add some zoom picture of fig. 3a in order to show the changes in coercivity.

We thank the reviewer for this suggestion. We think these parameters are far from our study and interests especially the magnetic properties of the synthesized nanocomposite are required only for the magnetic separation only after the adsorption process.

Reviewer 3 Report

This manuscript deals with the synthesis of a novel composite adsorptive material by modification of magnetic chitosan with polyethylenimine. The material is fully characterized in terms of properties that play a central role in the adsorption process. The results demonstrated that the prepared material is equally suitable for commonly found arsenic oxidation species. The paper is well prepared and easy to read and the content of the paper can attract scientific community. I have few suggestions of minor nature.

1. In the current form, the Introduction section comprises of one paragraph. I suggest subdividing the extremely long paragraph into small paragraphs that will enable the reader to extract useful information.
2. Superior materials for arsenic removal are iron oxides based on iron minerals such as akaganeite, goethite and feroxyhyte. For example, see the following, https://doi.org/10.1016/j.jhazmat.2020.123221. You have documented that copper oxide is frequently exercised for decontamination of arsenic-polluted waters.
3. Figure 6(a): As you have not used adsorption isotherms to describe the adsorption capacity of the material. I am wondering how you achieved the adsorption curve. Further, non-linear forms of the adsorption isotherms are generally applied to describe adsorption equilibrium data but you have applied non-linear forms. The authors shall discuss this in the manuscript.
4. Figure 5a and Figure 6a: The authors shall discuss why the adsorption capacities obtained through adsorption kinetic and isotherm data differ?

Author Response

In the current form, the Introduction section comprises of one paragraph. I suggest subdividing the extremely long paragraph into small paragraphs that will enable the reader to extract useful information.

The introduction was arranged as required by the reviewer

 Superior materials for arsenic removal are iron oxides based on iron minerals such as akaganeite, goethite and feroxyhyte. For example, see the following, https://doi.org/10.1016/j.jhazmat.2020.123221. You have documented that copper oxide is frequently exercised for decontamination of arsenic-polluted waters.

The data reported by Usman et al. (2020) was added in table 2. However, is very important to point out that the difference in the adsorbent efficiency between materials can be explained by the  applied operating conditions and the variability of the interactions between pollutants and the material functional groups. Generally,  strong interactions with the specific functional groups of the adsorbent surface permitted high adsorption capacity.

This statement was added in the text

 Figure 6(a): As you have not used adsorption isotherms to describe the adsorption capacity of the material. I am wondering how you achieved the adsorption curve. Further, non-linear forms of the adsorption isotherms are generally applied to describe adsorption equilibrium data but you have applied non-linear forms. The authors shall discuss this in the manuscript.

Linear and non-linear forms of the adsorption isotherms can be used and this depends on the experimental data and the value of the regression coefficient (R²). You can find the use of linear form in many studies.

 Figure 5a and Figure 6a: The authors shall discuss why the adsorption capacities obtained through adsorption kinetic and isotherm data differ?

 Fig.5a represents the time effect on the adsorption while Fig.6a represents the initial concentrations effect. So, the two figures must differ but at the similar conditions, the adsorption capacities are similar in the two figures.